Heat transfer device and an associated method of fabrication

ABSTRACT

A heat transfer device includes a casing and a wick disposed within the casing. The wick includes a first sintered layer and a second sintered layer. The first sintered layer includes a plurality of first sintered particles, having a first porosity and a plurality of first pores. The first sintered layer is disposed proximate to an inner surface of the casing. The second sintered layer includes a plurality of second sintered particles, having a second porosity and a plurality of second pores. The second sintered layer is disposed on the first sintered layer. The heat transfer device includes at least one first sintered particle smaller than at least one second pore and the first porosity is smaller than the second porosity.

This invention was made with Government support under contract numberN66001-08-C-2008 awarded by U.S. Department of Defense. The Governmenthas certain rights in the invention.

BACKGROUND

The present disclosure relates generally to a heat transfer device andmore particularly, to a vapor chamber or a heat pipe having a spatiallycontrolled porosity or pore size and an associated method offabrication.

A heat transfer device is used to transfer heat from a source to a sink.Such heat transfer devices may include a hot end and a cold end toenable transfer of the heat from the hot end to the cold end. Generally,the heat transfer device combines the principle of a thermalconductivity and a phase transition of a working fluid to transfer theheat. In one example, the heat transfer device is a sealed tube or asealed chamber, fabricated using a material having a high thermalconductivity. The heat transfer device includes the working fluid withinthe sealed chamber to transfer the heat effectively. Typically, suchheat transfer device may further include a wick to enable heat transferby condensation and evaporation of the working fluid i.e. by changingphase of the working fluid within the sealed chamber.

The conventional wick includes a plurality of mono-dispersed sinteredparticles distributed along the longitudinal direction of the heattransfer pipe. Typically wicks are designed to provide a high fluidtransport and phase change capability of the working fluid. Suchfunctions are achieved by designing the wick having a very large porescombined with high surface area for phase change processes. However,such conventional wicks are less effective in performing phase change ofthe working fluid, because the design and fabrication process are basedon mono-dispersed particles. Further, such wick structures provide solidconduction thermal resistance due to low contact area with the chamberwalls, or casing material and/or low porosity.

Such limitations can be addressed by designing the wick, having poresize variation through the use of varying particle sizes. However, thewicks that are designed with varying particle sizes are fabricated usingan organic carrier which is burned completely to generate the sinteredparticles having varied pore size and/or varied porosity. Suchfabrication processes may result in contamination of the heat transferdevice, limit the wick fabrication temperature to temperatures highenough to burn-away the organics, and also may lead to generation of anon-condensable fluid during prolonged operation of the heat transferdevice.

There is a need for an improved heat transfer device and a method forfabricating the heat transfer device.

BRIEF DESCRIPTION

In accordance with one exemplary embodiment, a heat transfer device isdisclosed. The heat transfer device includes a casing and a wickdisposed within the casing. The wick includes a first sintered layerdisposed proximate to an inner surface of the casing and a secondsintered layer disposed on the first sintered layer. The first sinteredlayer includes a plurality of first sintered particles, having a firstporosity and a plurality of first pores. The second sintered layerincludes a plurality of second sintered particles, having a secondporosity and a plurality of second pores. At least one first sinteredparticle is smaller than at least one second pore and the first porosityis smaller than the second porosity

In accordance with one exemplary embodiment, a method for manufacturinga heat transfer device is disclosed. The method includes filling amixture of a plurality of first particles and second particles within afirst half casing portion. Further, the method includes leveling theplurality of first and second particles within the first half casingportion. The method includes vibrating the first half casing portion tosegregate the plurality of first particles from the plurality of secondparticles such that a first layer portion having the plurality of firstparticles and a second layer portion having the plurality of secondparticles are formed. The first layer portion is disposed proximate toan inner surface of the first half casing portion and a second layerportion is disposed on the first layer portion. Further, the methodincludes sintering the first layer portion and the second layer portionto generate a first sintered layer portion and a second sintered layerportion. The first sintered layer portion includes a plurality of firstsintered particles, having a first porosity and a plurality of firstpores. The second sintered layer portion includes a plurality of secondsintered particles, having a plurality of second pores and a secondporosity greater than the first porosity. Further, the method includesforming at least one first sintered particle smaller than at least onesecond pore. The method further includes forming a first wick portionhaving the first sintered layer portion and the second sintered layer.The method further includes repeating the filling, the leveling, thevibrating, and the sintering process in a second half casing portion toform a second wick portion within the second half casing portion.Further, the method includes coupling the first half casing portion tothe second half casing portion such that the first wick portion iscoupled to the second wick portion to form a heat transfer device.

DRAWINGS

These and other features and aspects of embodiments of the presentdisclosure will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a schematic sectional view of a heat transfer device, forexample a vapor chamber in accordance with an exemplary embodiment;

FIG. 2 a is a sectional view of a first half casing portion of a vaporchamber in accordance with an exemplary embodiment;

FIG. 2 b is a sectional view of a second half casing portion of a vaporchamber in accordance with an exemplary embodiment;

FIG. 3 is a schematic sectional view of a portion of a vapor chamberhaving a first sintered layer, a second sintered layer, and a thirdsintered layer in accordance with an exemplary embodiment;

FIG. 4 a is a perspective view of a portion of a wick having a pluralityof first sintered particles and a plurality of second sintered particlesin accordance with an exemplary embodiment;

FIG. 4 b is a perspective view of the portion of the wick in FIG. 4 ahaving a plurality of third sintered particles in accordance with anexemplary embodiment;

FIG. 4 c is a perspective view of a portion of a wick having a pluralityof third sintered particles in accordance with another exemplaryembodiment;

FIG. 5 a is a schematic view of a portion of a wick having a firstsintered layer with a uniform thickness of and a second sintered layerhaving a non-uniform thickness in accordance with another exemplaryembodiment;

FIG. 5 b is a schematic view of the portion of the wick in FIG. 5 ahaving a third sintered layer having a non-uniform thickness inaccordance with another exemplary embodiment;

FIG. 6 is a schematic flow diagram illustrating a method ofmanufacturing a first sintered layer and a second sintered layer withina casing in accordance with an exemplary embodiment;

FIG. 7 is a schematic flow diagram illustrating a method ofmanufacturing a third sintered layer portion on a second sintered layerportion within a first half casing portion in accordance with anexemplary embodiment;

FIG. 8 is a schematic flow diagram illustrating a method ofmanufacturing a second sintered layer portion having a non-uniformthickness along an evaporator section, a transport section, and acondenser section in accordance with another exemplary embodiment;

FIG. 9 is a schematic flow diagram illustrating a method ofmanufacturing a second sintered layer portion having a non-uniformthickness along an evaporator section, a transport section, and acondenser section in accordance with yet another exemplary embodiment;and

FIG. 10 is a schematic flow diagram illustrating a method ofmanufacturing a third sintered layer portion having a non-uniformthickness along an evaporator section, a transport section, and acondenser section in accordance with another exemplary embodiment.

DETAILED DESCRIPTION

While only certain features of embodiments have been illustrated anddescribed herein, many modifications and changes will occur to thoseskilled in the art. It is, therefore, to be understood that the appendedclaims are intended to cover all such modifications and changes asfalling within the spirit of the invention.

Embodiments discussed herein disclose a heat transfer device andassociated methods for manufacturing the heat transfer device. Moreparticularly, certain embodiments disclose a vapor chamber. The vaporchamber includes a casing and a wick having a first sintered layer and asecond sintered layer disposed within the casing. The first sinteredlayer includes a plurality of first sintered particles having a firstporosity and a plurality of first pores. The first sintered layer isdisposed proximate to an inner surface of the casing. The secondsintered layer includes a plurality of second sintered particles havinga second porosity and a plurality of second pores. The second sinteredlayer is disposed on the first sintered layer. At least one firstsintered particle is smaller than at least one second pore and the firstporosity is smaller than the second porosity.

Certain embodiments disclose a method of manufacturing a heat transferdevice. More specifically, certain embodiments disclose a method ofmanufacturing a vapor chamber. The method includes filling a pluralityof first particles and second particles within a first half casingportion and leveling the plurality of first and second particles.Further, the method includes vibrating the first half casing portion soas to segregate the plurality of first particles from the plurality ofsecond particles to form a first layer portion and a second layerportion. The segregated first layer portion includes the plurality offirst particles disposed proximate to an inner surface of the first halfcasing portion and the segregated second layer portion includes theplurality of second particles disposed on the first layer portion. Themethod further includes sintering the first layer portion and the secondlayer portion to generate a first sintered layer portion and a secondsintered layer portion. The first sintered layer portion and the secondsintered layer portion together form a first wick portion.

Further, the method includes repeating the filling, the leveling, thevibrating, and the sintering process in a second half casing portion toform a second wick portion within the second half casing portion. Themethod further includes coupling the first half casing portion to thesecond half casing portion such that the first wick portion is coupledto the second wick portion to form the vapor chamber.

FIG. 1 is a schematic sectional view of a heat transfer device 100 inaccordance with an exemplary embodiment. In the illustrated embodiment,the heat transfer device 100 is a vapor chamber. It should be notedherein that the terms “heat transfer device” and “vapor chamber” areused interchangeably. In some other embodiments, the heat transferdevice is a heat pipe.

The vapor chamber 100 includes a casing 102 and a wick 104. Further, thewick forms a sealed chamber 106 filled with a working fluid 108. Theworking fluid 108 transfers the heat from one end 116 to another end 118of the vapor chamber 100. Further, the vapor chamber 100 includes anevaporator section 110 disposed proximate to the end 116, a condensersection 112 disposed proximate to the end 118, and a transport section114 disposed between the evaporator section 110 and the condensersection 112. The evaporator section 110 is used to absorb heat from asource (not shown in FIG. 1) by evaporating the working fluid 108. Thecondenser section 112 is used to release heat to a sink (not shown inFIG. 1) by condensing the working fluid 108. The transport section 114is used to conduct the heat from one end 116 to the other end 118 viathe working fluid 108. The vapor chamber 100 is fabricated using amaterial having high thermal conductivity. The material of the vaporchamber 100 may be copper or aluminum nitrate, for example. The vaporchamber 100 has a rectangular shape and a length “L₁” in the range offive to ten meters, for example.

The casing 102 includes a first half casing portion 102 a and a secondhalf casing portion 102 b. Each half casing portion 102 a, 102 bincludes an inner surface 120 and an outer surface 122. Each half casingportion 102 a, 102 b has a U-shape. The first half and second halfcasing portions 102 a, 102 b are coupled to each other by brazing,soldering, or the like. The wick 104 is disposed proximate to the innersurface 120 of the casing 102. The wick 104 includes a first sinteredlayer 126 and a second sintered layer 128. Specifically, the firstsintered layer 126 is disposed proximate to the inner surface 120 of thecasing 102. The second sintered layer 128 is disposed on the firstsintered layer 126. The first sintered layer 126 includes a firstsintered layer portion 126 a disposed in the first half casing portion102 a and another first sintered layer portion 126 b disposed in thesecond half casing portion 102 b. Similarly, the second sintered layer128 includes a second sintered layer portion 128 a disposed on the firstsintered layer portion 126 a and another second sintered layer portion128 b disposed on the other first sintered layer portion 126 b.

The first and second sintered layers 126, 128 have a uniform thickness“T₁” and “T₂” respectively across the length “L₁” of the vapor chamber100. The casing 102 may be made of a first material and the firstsintered layer 126 and the second sintered layer 128 are made of asecond material different from the first material. The casing 102, thefirst sintered layer 126, and the second sintered layer 128 may be madeof the same material.

FIG. 2 a is a sectional view along (2A-2A) of the first half casingportion 102 a in accordance with the embodiment of FIG. 1. The firsthalf casing portion 102 a includes a first wick portion 104 a and acoating portion 130 a.

The first wick portion 104 a includes the first sintered layer portion126 a disposed proximate to the inner surface 120 of the first halfcasing portion 102 a and the second sintered layer portion 128 adisposed on the first sintered layer portion 126 a. The coating portion130 a is disposed between the inner surface 120 of the first half casingportion 102 a and the first sintered layer portion 126 a. The coatingportion 130 a may include one or more layers depending on theapplication and design criteria. The coating portion 130 a may be madeof a material having high thermal conductivity such as copper, aluminumnitrate, or the like. The first half casing portion 102 a may be made ofa first material and the coating portion 130 a, the first sintered layerportion 126 a, and the second sintered layer portion 128 a may be madeof a second material different from the first material.

FIG. 2 b is a sectional view along (2B-2B) of the second half casingportion 102 b in accordance with the embodiment of FIG. 1. The secondhalf casing portion 102 b includes a second wick portion 104 b and acoating portion 130 b.

The second wick portion 104 b includes the first sintered layer portion126 b disposed proximate to the inner surface 120 of the second halfcasing portion 102 b and the second sintered layer portion 128 bdisposed on the first sintered layer portion 126 b. The coating portion130 b is disposed between the inner surface 120 of the second halfcasing portion 102 b and the first sintered layer portion 126 b. Thecoating portion 130 b includes a material having high thermalconductivity such as copper, aluminum nitrate, or the like. The secondhalf casing portion 102 b may be made of a first material and thecoating portion 130 b, the first sintered layer portion 126 b, and thesecond sintered layer portion 128 b may be made of a second materialdifferent from the first material.

FIG. 3 is a schematic sectional view of a portion of the vapor chamber100. In the illustrated embodiment, the vapor chamber 100 includes thecasing 102, the first sintered layer 126, the second sintered layer 128,and additionally a third sintered layer 140. The third sintered layer140 is disposed on the second sintered layer 128. The third sinteredlayer 140 has a uniform thickness “T₃” along the length of the vaporchamber 100. The third sintered layer 140 includes a material havinghigh thermal conductivity, such as copper, aluminum nitrate, or thelike.

FIG. 4 a is a perspective view of a portion 134 of the wick 104. Thewick 104 includes the first sintered layer 126 and the second sinteredlayer 128. The first sintered layer 126 has a plurality of firstsintered particles 142 and the second sintered layer 128 has a pluralityof second sintered particles 144. Further, the first sintered layer 126has a plurality of first pores 146 and a first porosity 148 and thesecond sintered layer 128 has a plurality of second pores 150 and asecond porosity 152.

Each first sintered particle 142 has a size “S₁” and each secondsintered particle 144 has a size “S₂”. Each first sintered particle 142has the size “S₁” in a range of hundred nanometers to fifty micrometersand each second sintered particle 144 has the size “S₂” in a range often micrometers to hundred micrometers. The size “S₂” of each secondsintered particle 144 is greater than the size “S₁” of each firstsintered particle 142.

Further, each first pore 146 has a size “S₃” and each second pore 150has a size “S₄”. Each first pore 146 has the size “S₃” in a range of tennanometers to ten micrometers and each second pore 150 has the size “S₄”in a range of one micrometer to fifty micrometers. Each first sinteredparticle 142 and each second sintered particle 144 has a spherical oroval or circular shape. The size “S₁” of each first sintered particle142 is smaller than the size “S₄” of each second pore 150. The size “S₁”of the first sintered particle 142 is at least forty to sixty percentsmaller than the size “S₄” of the second pore 150. The first sinteredparticle 142 having a relatively smaller size than the second pore 150provides higher heat transfer capability and offers very less thermalresistance along the length of the vapor chamber 100.

The first porosity 148 of the first sintered layer 126 is in a range offive percent to forty percent. The second porosity 152 of the secondsintered layer 128 is in a range of eight percent to twenty percent. Thefirst porosity 148 is smaller than the second porosity 152. The secondlayer 128 having a relatively greater second porosity 152 facilitates toexert a higher capillary pressure on the working fluid along the lengthof the vapor chamber 100.

FIG. 4 b is a perspective view of the third sintered layer 140 inaccordance with the exemplary embodiment of FIG. 4 a. The third sinteredlayer 140 includes a plurality of third sintered particles 154. Theplurality of third sintered particles 154 is disposed on the pluralityof second sintered particles 144. Each third sintered particle 154 has adendrite shape. Further, the third sintered layer 140 has a plurality ofthird pores 156 and a third porosity 158. Each third sintered particle154 has a size “S₅” and each third pore 156 has a size “S₆”. Each thirdsintered particle 154 has the size “S₅” in a range of hundred nanometersto ten micrometers and each third pore 156 has a size “S₆” in a range ofone nanometer to ten micrometers. The third porosity 158 is in a rangeof twenty percent to eighty percent. The size “S₅” of each thirdsintered particle 154 is smaller or equal to the size “S₂” of eachsecond sintered particle 144 and the third porosity 158 is smaller thanthe second porosity 152. The third sintered layer 140 having arelatively smaller third porosity 152 provides a higher heat transfercapability of the wick 104.

FIG. 4 c is a perspective view of a third sintered layer 139 inaccordance with another exemplary embodiment. The third sintered layer139 is disposed on a second sintered layer (not shown in FIG. 4 c). Thethird sintered layer 141 includes a plurality of third particles 132having a spherical shape.

FIG. 5 a is a schematic view of a portion 137 of a wick 105 having afirst sintered layer 127 and a second sintered layer 129 in accordancewith another exemplary embodiment.

The second sintered layer 129 is disposed on the first sintered layer127. The first sintered layer 127 has a uniform thickness “T₄” along anevaporator section 111, a condenser section 113, and a transport section115 of a vapor chamber. The second sintered layer 129 has a non-uniformthickness along the evaporator section 111, the condenser section 113,and the transport section 115. Specifically, the second sintered layer129 has a thickness “T₅” corresponding to the evaporator section 111, athickness “T6” corresponding to the condenser section 113, and athickness “T₇” corresponding to the transport section 115. The thickness“T₅” may be in the range of five millimeters to ten millimeters, thethickness “T₆” may be in the range of two millimeters to fivemillimeters, and the thickness “T₇” may be in the range of fivemillimeters to eight millimeters, for example. The thickness “T₅” isgreater than the thickness “T₆”. The thickness “T₇” is greater than thethickness “T₅”.

FIG. 5 b is a schematic view of the portion 137 of the wick 105 havingan additional third sintered layer 141 in accordance with the exemplaryembodiment of FIG. 5 a.

The third sintered layer 141 is disposed on the second sintered layer129. The third sintered layer 141 has a non-uniform thickness along theevaporator section 111, the condenser section 113, and the transportsection 115 of the vapor chamber. Specifically, the third sintered layer141 has a thickness “T₈” corresponding to the evaporator section 111, athickness “T₉” corresponding to the condenser section 113 and athickness “T₁₀” corresponding to the transport section 115. Thethickness “T₈” may be in the range of two millimeters to threemillimeters, the thickness “T₉” may be in the range of one millimeter totwo millimeters, and the thickness “T₁₀” may be in the range of twomillimeters to five millimeters, for example. The thickness “T₈” isgreater than the thickness “T₉”. The thickness “T₁₀” is greater than thethickness “T₈”.

FIG. 6 is a schematic flow diagram illustrating a plurality of stepsinvolved in a method 160 of manufacturing the first sintered layer 126and the second sintered layer 128 within the casing 102 in accordancewith the embodiment of FIGS. 1, 2 a, and 2 b.

The method 160 includes a step 162 of disposing the first half casingportion 102 a and a step 168 of applying the coating portion 130 a onthe inner surface 120 of the first half casing portion 102 a. Aplurality of first particles 164 and a plurality of second particles 166are filled in the first half casing portion 102 a. The first half casingportion 102 a is made of a first material and the coating portion 130 a,the plurality of first particles 164, and the plurality of secondparticles 166 includes a second material different from the firstmaterial.

In another embodiment, a coating portion 130 a may not be applied to theinner surface 120 of the first half casing portion 102 a and theplurality of particles 164, 166 are filled directly within the firsthalf casing portion 102 a such that the plurality of particles 164, 166are in contact with the inner surface 120 of the first half casingportion 102 a. The first half casing portion 102 a, the plurality offirst particles 164, and the plurality of second particles 166 includethe same material.

A step 170 includes leveling the plurality of first particles 164 andthe plurality of second particles 166 within the first half casingportion 102 a. The plurality of first and second particles 164, 166 isleveled using a squeegee device 172. A uniform contact surface 171 ofthe squeegee device 172 is used to level the plurality of firstparticles 164 and the plurality of second particles 166 to generate auniform thickness. The squeegee device 172 may be made of a materialsuch as nickel-cobalt ferrous alloy or ceramics such as aluminumnitrate, alumina, silicon carbide, silicon nitride or the like.

The method 160 further includes a step 174 of vibrating the first halfcasing portion 102 a to segregate the plurality of first particles 164from the plurality of second particles 166 such that a first layerportion 176 a and a second layer portion 178 a is formed within thefirst half casing portion 102 a. The first half casing portion 102 a isvibrated using a vibrator device 180. The vibrator device 180 is clampedto the first half casing portion 102 a and powered via mechanicalelements to vibrate the first half casing portion 102 a. The first layerportion 176 a having the plurality of first particles 164 is disposedproximate to the inner surface 120 of the first half casing portion 102a and the second layer portion 178 a having the plurality of secondparticles 166 is disposed on the first layer portion 176 a. The firstlayer portion 176 a has a uniform thickness “T₀₁” and the second layerportion 178 a has a uniform thickness “T₀₂”. In another exemplaryembodiment, the step 174 of vibrating the half casing portion may beoptional.

The method 160 further includes a step 182 of sintering the first layerportion 176 a and the second layer portion 178 a. The step 182 includesdisposing a sintering spacer 184 over the second layer portion 178 a andfilling an additional amount of the plurality of second particles 166 inthe spaces formed between the sintering spacer 184 and the inner surface120 of the first half casing portion 102 a. The sintering spacer 184 hasa uniform contact surface 187 contacting the second layer portion 178 a.The step 182 further includes disposing the first half casing portion102 a with the sintering spacer 184, in a sintering device 188 to sinterthe first layer portion 176 a and the second layer portion 178 a so asto generate the first sintered layer portion 126 a and the secondsintered layer portion 128 a having a uniform thickness as shown in step190.

The first sintered layer portion 126 a includes the plurality of firstsintered particles 142 having the first porosity 148 and the pluralityof first pores 146 (as shown in FIG. 4 a). The second sintered layerportion 128 a includes the plurality of second sintered particles 144having the plurality of second pores 150 and the second porosity 152 (asshown in FIG. 4 a). The sintering step 182 is performed in a controlledenvironment i.e. at a predefined temperature and pressure so as togenerate at least one first sintered particle 142 smaller than at leastone second pore 150. The sintering process is controlled to generate atleast forty to sixty percent of the first sintered particles 142 havinga size smaller than the plurality of second pores 150. The sinteringpressure is in a range of 50 bars to 60 bars and the sinteringtemperature is in a range of 648.89 degrees Celsius to 815.56 degreesCelsius. The sintering spacer 184 may be made of a material such asnickel-cobalt ferrous alloy or ceramics including aluminum nitrate,alumina, silicon carbide, and silicon nitride.

The first sintered layer 126 a has a uniform thickness “T₁”corresponding to an evaporator section 110, a condenser section 112, anda transport section 114. Similarly, the first sintered layer 128 a has auniform thickness “T₂” corresponding to the evaporator section 110, thecondenser section 112, and the transport section 114. The step 190further involves removing the sintering device 188 and the sinteringspacer 184 such that the first wick portion 104 a is formed within thefirst half casing portion 102 a. The first wick portion 104 a includesthe first sintered layer portion 126 a and the second sintered layerportion 128 a.

Similarly, the method further includes a step 192 of repeating the steps162, 168, 170, 174, 182, and 190 in the second half casing portion 102 bto form a second wick portion 104 b. The second wick portion 104 bincludes the first sintered layer portion 126 b disposed proximate tothe inner surface 120 of the second half casing portion 102 b and thesecond sintered layer portion 128 b disposed on the first sintered layerportion 126 b. The method also includes applying the coating portion 130b on the inner surface 120 of the second half casing portion 102 a.

The method 160 further includes a step 194 of coupling the first halfcasing portion 102 a to the second half casing portion 102 b such thatthe first wick portion 104 a is coupled to the second wick portion 104 bto form the heat transfer device 100. A sealed chamber 106 is formedbetween the first half casing portion 102 a and the second half casingportion 102 b. The heat transfer device 100 includes a casing 102 havinga wick 104 disposed within the casing 102. The first half and secondhalf casing portions 102 a, 102 b are coupled to each other by brazing,soldering, or the like.

FIG. 7 is a schematic flow diagram illustrating the method 360 ofmanufacturing an additional third sintered layer portion 140 a on thesecond sintered layer portion 128 a within the first half casing portion102 a in accordance with the embodiment of FIGS. 2 a, 2 b, and 3.

The method 360 includes a step 196 of disposing the first half casingportion 102 a having the first sintered layer portion 126 a and thesecond sintered layer portion 128 a. The method 360 further includes astep 200 of filling the plurality of third particles 198 within thefirst half casing portion 102 a. Specifically, the plurality of thirdparticles 198 are filled on the second sintered layer portion 128 a. Themethod 360 further includes a step 202 of leveling the plurality ofthird particles 198 within the first half casing portion 102 a so as toform a third layer portion 204 a having a uniform thickness T₀₃. Thesqueegee device 172 having the uniform contact surface 171 is used forleveling the plurality of third particles 198.

The method 360 further includes a step 206 of sintering the third layerportion 204 a. The sintering step 206 includes disposing the sinteringspacer 184 on the third layer portion 204 a and disposing the first halfcasing portion 102 a including the sintering spacer 184, in thesintering device 188 to sinter the third layer portion 204 a so as togenerate the third sintered layer portion 140 a. The sintering spacer184 having a uniform contact surface 187, is used to generate the thirdsintered layer portion 140 a having the uniform thickness “T₃”. Thethird sintered layer portion 140 a includes the plurality of thirdsintered particles 154 having the third porosity 158 and the pluralityof third pores 156 (as shown in FIG. 4 b). The sintering process isperformed in a controlled environment so as to generate the thirdporosity 158 smaller than the second porosity 152. The third sinteredparticle 154 has a size less than or equal to the size of the secondsintered particle 144.

The steps 196, 200, 202, and 206 are repeated in the second half casingportion 102 b to generate another third sintered layer portion 140 b.

FIG. 8 is a flow diagram illustrating a method 208 of manufacturing thesecond sintered layer portion 129 a having a non-uniform thickness inaccordance with the embodiment of FIG. 5 a.

The method 208 includes a step 210 of forming a second layer portion 179a having a non-uniform thickness on a first layer portion 177 a having auniform thickness “T₀₄”. The step 210 includes leveling a plurality ofsecond particles 167 using a squeegee spacer 212 having a uniformcontact surface 214. Two smaller squeegee spacers 173, 175 are disposedon the second layer portion 179 a corresponding to the position of theevaporator section 111 and the condenser section 113. The squeegeespacer 212 is disposed on the second layer portion 179 a and contactingthe two smaller squeegee spacers 173, 175 so as to form the second layerportion 179 a having a non-uniform thickness. The second layer portion179 a has a thickness “T₀₅” for the evaporator section 111, a thickness“T₀₆” for the condenser section 113, and a thickness “T₀₇” for thetransport section 115. The squeegee spacers 212, 173, 175 may be made ofa material including nickel-cobalt ferrous alloy or ceramics such asaluminum nitrate, alumina, silicon carbide, and silicon nitride.

The method 208 further includes a step 216 of generating the secondsintered layer portion 129 a having a non-uniform thickness over thefirst sintered layer portion 127 a having the uniform thickness “T₄”.The step 216 includes replacing the squeegee spacer 212 with a firstsintering spacer 213 having a uniform contact surface 218 and the twosmaller squeegee spacers 173, 175 with second sintering spacers 183,185. The process further includes sintering the second layer portion 179a having non-uniform thickness to form the second sintered layer portion129 a. The second sintered layer portion 129 a has the thickness “T₅”for the evaporator section 111, the thickness “T₆” for the condensersection 113, and the thickness “T₇” for the transport section 115. Thesintering spacers 213, 183, 185 may be made of a material includingnickel-cobalt ferrous alloy or ceramics such as aluminum nitrate,alumina, silicon carbide, and silicon nitride.

FIG. 9 is a flow diagram illustrating a method 220 for manufacturing asecond sintered layer portion 229 a having a non-uniform thickness inaccordance with another embodiment.

The method 220 includes a step 222 for forming a second layer portion228 a having a non-uniform thickness, using a squeegee device 226 havinga non-uniform contact surface 224. The non-uniform contact surface 224of the squeegee device 226 is disposed over the second layer portion 228a and the squeegee device 226 is actuated so as to form the second layerportion 228 a having a non-uniform thickness. The second layer portion228 a has a thickness “T₀₁₁” corresponding to the position of anevaporator section 221, a thickness “T₀₁₂” corresponding to the positionof a condenser section 223, and a thickness “T₀₁₃” corresponding to theposition of a transport section 225. The squeegee device 226 having thenon-uniform contact surface 224 may be manufactured by milling.

The method 220 further includes a step 230 of generating the secondsintered layer portion 229 a having a non-uniform thickness. The process230 includes replacing the squeegee device 226 with a sintering spacer232 having a non-uniform contact surface 234 and sintering the secondlayer portion 228 a in a sintering device to form the second sinteredlayer portion 229 a having the non-uniform thickness. The secondsintered layer portion 229 a has a thickness “T₁₁” corresponding to theevaporator section 221, a thickness “T₁₂” corresponding to the positionof the condenser section 223, and a thickness “T₁₃” corresponding to theposition of the transport section 225. The sintering spacer 232 havingthe non-uniform contact surface 234 may also be manufactured by milling

FIG. 10 is a schematic flow diagram illustrating a method 236 ofmanufacturing a third sintered layer portion 141 a having a non-uniformthickness in accordance with the embodiment of FIG. 5 b.

The method 236 includes a step 238 of forming a third layer portion 240a having a non-uniform thickness. A plurality of third particles 246 isdisposed on the second sintered layer portion 129 a. A squeegee device244 having a non-uniform contact surface 242, is actuated over theplurality of third particles 246 so as to form a third layer portion 240a having a non-uniform thickness. The third layer portion 240 a has athickness “T₀₈” corresponding to the position of the evaporator section111, a thickness “T₀₉” corresponding to the position of the condensersection 113, and a thickness “T₀₁₀” corresponding to the position of thetransport section 115. The method 236 further includes a step 248 ofgenerating the third sintered layer portion 141 a having a non-uniformthickness. The step 248 includes replacing the squeegee device 244 witha sintering spacer 252 having a non-uniform surface 254 for sinteringthe third layer portion 240 a to form the third sintered layer portion141 a. The third sintered layer portion 141 a has the thickness “T₈”corresponding to the position of the evaporator section 111, thethickness “T₉” corresponding to the position of the condenser section113, and the thickness “T₁₀” corresponding to the position of thetransport section 115.

Embodiments of the present disclosure discussed herein facilitate easyand economic manufacturing of the heat transfer device. Further, theheat transfer device of the present disclosure provides lower thermalresistance, higher thermal conductivity, and higher heat transportcapability.

1. A heat transfer device comprising: a casing having an inner surfaceand an outer surface; and a wick disposed within the casing; wherein thewick comprises: a first sintered layer comprising a plurality of firstsintered particles, having a first porosity and a plurality of firstpores, disposed proximate to the inner surface of the casing; and asecond sintered layer comprising a plurality of second sinteredparticles, having a second porosity and a plurality of second pores,disposed on the first sintered layer; wherein at least one firstsintered particle is smaller than at least one second pore and the firstporosity is smaller than the second porosity.
 2. The heat transferdevice of claim 1, wherein each first pore has a size in a range of tennanometers to ten micrometers.
 3. The heat transfer device of claim 1,wherein each second pore has a size in a range of one micrometer tofifty micrometers.
 4. The heat transfer device of claim 1, wherein eachfirst sintered particle has a size in a range of hundred nanometers tofifty micrometers.
 5. The heat transfer device of claim 1, wherein eachsecond sintered particle has a size in a range of ten micrometers tohundred micrometers.
 6. The heat transfer device of claim 1, wherein thefirst porosity is in a range of five percent to forty percent.
 7. Theheat transfer device of claim 1, wherein the second porosity is in arange of eight percent to twenty percent.
 8. The heat transfer device ofclaim 1, wherein the wick further comprises a third sintered layerincluding a plurality of third sintered particles, having a thirdporosity and a plurality of third pores, disposed on the second sinteredlayer
 9. The heat transfer device of claim 8, wherein each third porehas a size in a range of one nanometer to ten micrometers.
 10. The heattransfer device of claim 8, wherein the third porosity is in a range oftwenty percent to eighty percent.
 11. The heat transfer device of claim8, wherein each third sintered particle has a size in a range of hundrednanometers to ten micrometers.
 12. The heat transfer device of claim 8,wherein a size of each third sintered particle is less than or equal toa size of each second sintered particle.
 13. The heat transfer device ofclaim 8, wherein the casing, the plurality of first sintered particles,the plurality of second sintered particles, and the plurality of thirdsintered particles comprise a same material.
 14. The heat transferdevice of claim 1, wherein the first sintered layer is disposedcontacting the inner surface of the casing.
 15. The heat transfer deviceof claim 1, further comprising a coating disposed between the firstsintered layer and the inner surface of the casing.
 16. The heattransfer device of claim 15, wherein the casing comprises a firstmaterial and the first sintered layer, the second sintered layer, andthe coating comprises a second material different from the firstmaterial.
 17. The heat transfer device of claim 1, further comprising anevaporator section, a transport section, and a condenser section withinthe casing, wherein the wick has a uniform thickness extending along theevaporator section, the transport section, and the condenser section.18. The heat transfer device of claim 1, further comprising anevaporator section, a transport section, and a condenser section withinthe casing, wherein the wick has a non-uniform thickness extending alongthe evaporator section, the transport section, and the condensersection.
 19. A method comprising: filling a plurality of particleswithin a first half casing portion, wherein the plurality of particlescomprises a plurality of first particles and a plurality of secondparticles; leveling the plurality of first and second particles withinthe first half casing portion; vibrating the first half casing portionto segregate the plurality of first particles from the plurality ofsecond particles such that a first layer portion having the plurality offirst particles, is disposed proximate to an inner surface of the firsthalf casing portion and a second layer portion having the plurality ofsecond particles is disposed on the first layer portion; sintering thefirst layer portion and the second layer portion to generate a firstsintered layer portion including a plurality of first sinteredparticles, having a first porosity and a plurality of first pores, and asecond sintered layer portion including a plurality of second sinteredparticles, having a plurality of second pores and a second porositygreater than the first porosity, wherein at least one first sinteredparticle is smaller than at least one second pore, and the firstsintered layer portion and the second sintered layer portion togetherform a first wick portion; repeating the filling, the leveling, thevibrating, and the sintering process in a second half casing portion toform a second wick portion within the second half casing portion; andcoupling the first half casing portion to the second half casing portionsuch that the first wick portion is coupled to the second wick portionto form a heat transfer device.
 20. The method of claim 19, wherein theleveling further comprises forming a uniform thickness of the pluralityof first and second particles along an evaporator section, a transportsection, and a condenser section of the first half casing portion. 21.The method of claim 19, wherein the leveling further comprises forming anon-uniform thickness of the plurality of first and second particlesalong an evaporator section, a transport section, and a condensersection of the first half casing portion.
 22. The method of claim 19,wherein the sintering further comprises disposing a sintering spacerhaving a non-uniform contact surface on the second layer portion. 23.The method of claim 19, wherein the sintering further comprises:disposing a first sintering spacer having a uniform contact surface onthe second layer portion; and disposing at least one second sinteringspacer between the uniform contact surface of the first sintering spacerand the second layer portion.
 24. The method of claim 19, furthercomprises performing filling, leveling, and sintering of a third layerportion having a plurality of third particles disposed on the secondsintered layer portion to generate a third sintered layer portionincluding a plurality of third sintered particles, having a plurality ofthird pores, and a third porosity, on the second sintered layer portion,wherein a size of each third sintered particle is less than or equal toa size of each second sintered particle.
 25. The method of claim 19,further comprising applying a coating on the inner surface of the firsthalf casing portion before filling the plurality of first and secondparticles in the first half casing portion, wherein the first halfcasing portion comprises a first material and the plurality of first andsecond particles and the coating comprise a second material differentfrom the first material.